The invention relates to set-screw retention of a bearing ring, such as the inner race ring of an antifriction bearing, to a shaft, for hopefully fixed antirotational engagement to the shaft.
Antifriction bearings used in fans, blowers, conveyors and other industrial machinery are frequently slide-fitted (i.e., loosely fitted) into position on straight shafting and locked to the shaft by means of set screws. Set screws are thread-mounted into tapped holes in the inner ring of such a bearing, with a non-interference fit, generally a clearance in the order of 0.002 inch, because an interference fit can give rise to such local stress as to rupture the ring, it being noted that generally the pitch diameter of threads in the tapped hole is greater than inner-ring thickness, i.e., greater than depth of the tapped hole.
Orlomoski, U.S. Pat. No. 3,517,717 discloses self-locking screws with threads having yieldable rib formations for such interference fit to tapped holes as to effectively lock a screw against looseness, virtually regardless of the vibratory (or rotating) and load environment to which the parts secured by the screw may be subjected. But the use of threads with yieldable rib formations presents a problem for bearing-ring mounting to a shaft, because conventional specifications for the interference fit of such screws call for such high interference as offer unpredictable set-screw holding ability. High interference suggests the prospect of great holding ability, but this is a delusion if, as is the fact with current specifications, the torque needed to advance the high-interference set-screw fit is anything like the maximum torque to which the inner bearing ring can be safely subjected. There is thus uncertainty as to whether the encountered torque is that of binding the set-screw point to the shaft or is that of advancing the set screw in the tapped hole. With such uncertainty, the value of interference fit via yieldable thread formations can be lost, and what the machinist may have thought was a good setting torque for binding the inner ring to the shaft may turn out to be an ineffective, inadequate and destructive fit, destructive of the parts, of bearing life, and of production time for the involved machine.